1. Field of the Invention
The present disclosure relates generally to reserve electrical power sources, and more particularly, to reserve power sources for munitions such as air dropped weapons and projectiles fired by guns, mortars and the like, that are initiated during the deployment of munitions to generate power from internally stored mechanical potential energy and when applicable, used to indicate certain events that can be used to achieve safe and arm functionalities or the like.
2. Prior Art
Chemical reserve batteries have long been used in various munitions, weapon systems and other similar applications in which electrical energy is required over relatively short periods of times. In addition, unique to the military is the need for munitions batteries that may be stored for up to twenty years without maintenance. Reserve batteries are batteries designed to be stored for years, even decades, without performance degradation. Reserve batteries are stored in an inert state and can be activated within a fraction of a second with no degradation of battery capacity or power. Typical Reserve batteries are thermal batteries and liquid reserve batteries.
The typical liquid reserve battery is kept inert during storage by keeping the electrolyte separate from the electrodes. The electrolyte is kept in a glass or metal ampoule inside the battery case. Prior to use, the battery is activated by breaking the ampoule and allowing the electrolyte to flood the electrodes. The ampoule is broken either mechanically or by the high g shock experienced from being shot from the cannon.
Thermal batteries represent a class of reserve batteries that operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive.
Reserve batteries are expensive to produce, primarily since the process of their manufacture is highly labor intensive and involve mostly manual assembly. For example, the process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand. The reserve batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. In munitions, thermal batteries may be initiated during launch via inertial or electrical igniters, or may be initiated later during the flight via electrical igniters. The liquid reserve batteries are usually activated during launch by breaking the electrolyte ampoule.
Chemical reserve batteries, including thermal batteries and liquid reserve batteries, are generally very expensive to produce, require specialized manufacturing processes and equipment and quality control, and are generally required to be developed for each application at hand.
All existing and future smart and guided weapons, including gun-fired projectiles, mortars, and small and large gravity dropped weapons, require electric energy for their operation. For many fuzing operations such as fuzing “safe” and “arm” (S&A) and sensory functionalities and many other “smart” fuzing and initiation functionalities, the amount of electrical energy that is needed is low and may be as low as 10-50 mJ, and even less. In fact, with such electrical energy levels, low-power electronics could be easily powered to provide the above fuzing or the like functionalities. The amount of power required to operate many other electronic components, for example those used for diagnostics and health monitoring purposes, or for receiving a communicated signal or the like is also very small and can be readily achieved with electrical energy in the above range. In all such applications, particularly for powering electronics for fuzing and other similar “safe” and “arm” functionalities, it is highly desirable to have low-cost and safe alternatives to chemical reserve batteries. This is particularly the case for the above applications since it is generally difficult to produce very small, miniature, reserve batteries of any kind.
A need therefore exists for alternatives to chemical reserve batteries for low power applications such as fuzing electronics for “safe” and “arm” and other functionalities, and other similar low power applications. For munitions applications, such “reserve” type power sources have to have a very long shelf life of up to 20 years; be low cost; and be capable of being scaled to the required power level requirements, shape and size, with minimal design and manufacturing change efforts.
An objective is to provide non-chemical “reserve” type of power sources for the aforementioned and the like low power applications. In these power sources, mechanical potential energy can be stored in the power source and used to generate electrical energy upon occurrence of certain events, such as firing of a projectile by a gun or by the release (or ejection) of a gravity dropped weapon. This is in contrast to chemical reserve batteries in which stored chemical energy is released upon a certain event (such as firing by a gun or by an electrical charge), thereby allowing the battery to provide electrical energy.
Hereinafter, and since the source of energy in the disclosed power sources can be mechanical potential energy, these power sources are referred to as “mechanical reserve power sources”.
Here, a means of storing potential mechanical energy can be elastic deformation, such as in various types of spring elements and/or the structural flexibility of the structure of the projectile or gravity dropped weapon or the like, and not potential energy due to gravity. It is, however, appreciated by those skilled in the art that potential energy may also be stored by other means such as by pressurizing compressible fluids such as air. The mechanical potential energy stored in the “mechanical reserve power sources” can then be released via certain mechanisms to be described later in this disclosure upon the occurrence of certain intended event(s), such as firing and/or spinning of a projectile or releasing of a gravity-dropped weapon or other events appropriate to the device employing the power source. The released potential energy can then be used to generate electrical energy using well known methods such as by the use of active materials based elements such as piezoelectric elements or magnet and coil type generators. To this end, the mechanical stored potential energy is preferably used to generate vibration of certain mass-spring element(s). The vibration energy is then transformed into electrical energy by one of the aforementioned piezoelectric, coil and magnet or the like elements. Alternatively, stored mechanical potential energy is used to cause a continuous (such as rotary) motion of an inertial element (e.g., an inertial wheel type element) in the form of kinetic energy. The kinetic energy can then be converted to electrical energy using well known magnet and coil type generators or any other type of available mechanical to electrical energy conversion devices (generators).
A second object is to provide methods and apparatus for releasing the stored potential energy in the disclosed “mechanical reserve power sources” using various events such as gun firing acceleration (the so-called setback acceleration) of a projectile; deceleration of gun-fired projectile (the so-called set-forward acceleration); the process and/or mechanism of releasing (e.g., gravity dropping) the weapon from its mounting rack or the like; pulling out or ejection of a releasing element (e.g., a releasing pin or wire); etc.
For the mechanical reserve power sources employing piezoelectric elements for converting mechanical energy of vibration to electrical energy, methods described for mass-spring systems used in the piezoelectric based power generators described in the U.S. Pat. Nos. 7,231,874 and 7,312,557 can generally be used in the construction of the disclosed mechanical reserve power sources, particularly for those mechanical reserve power sources to be used in gun-fired projectiles and mortars which are subject to very high-G firing acceleration levels.
In addition, in such mechanical reserve power sources, the piezoelectric elements (stacks) employed to convert mechanical energy of vibration to electrical energy may also be used as sensors to measure setback and set-forward acceleration levels, target impact impulse levels and direction, the time of such events and more as described in the patent application publication number 2007-0204756 filed on Jan. 17, 2007, the contents of which is incorporated herein by reference. In this regard, it is important to note that all existing and future smart and guided projectiles can be equipped with means for sensing one or preferably more of the firing setback and set-forward accelerations, radial accelerations, flight vibration in the longitudinal and lateral (radial) directions, and terminal point impact induced acceleration. The measurements can include the related acceleration profiles. The sensory information can be used for guidance and control purposes as well as for fuze safety and operation.
A third object is to provide methods for using the disclosed mechanical reserve power sources as the means to provide for safety in general, and “safe” and “arm” functionalities in particular, for fuzing and other similar applications in gun-fired projectiles, mortars as well as gravity dropped weapons.
A fourth object is to provide methods for allowing the disclosed mechanical reserve type power sources that rely on conversion of the stored potential energy to vibration energy and consequent conversion of the vibration energy to electrical energy to continue to harvest energy from vibration and other oscillatory motions of the weapon, from aerodynamically induced vibrations, etc., during the flight.